I have a HP DeskJet 1220C, a PSC-950, and several other 900 series printers.
I've tried many types of inks and refill techniques and have had good luck
with the Inktec brand of refill kits and inks.
Here are some links you might find useful:
Factory website:
http://www.inktec.com/english/
The Inktec tools are excellent; the #45 kit comes with reusable silicone
rubber plugs to reseal the fill hole and a vacuum syringe fixture for
removing the air in the ink bladder bag. The #78 kit also comes with a
vacuum tool to extract the air out of the ink chambers which is critical to
getting the #78 to work again.
Check out this excellent German site for some interesting pictures of the
cartridges, instructions on how to refill, etc.
http://site0815.piranho.de/
On the #78s, I prefer drilling holes in the side of the cartridge to refill
the foam pads; overfilling these cartridges is fatal to proper operation.
If you want the instructions, I go to
http://groups.google.com and search
for 'C6578D refill success'. Thanks to Steve Bradshaw for developing and
posting this technique.
With some practice, you'll be able to refill cartridges in minutes with good
success. However, don't expect the every cartridges you fill to work
perfectly. (I can give some other advice as well - don't fill cartridges in
the kitchen sink, don't get ink in bathroom tile grout, use rubber gloves,
have plenty of paper towels on hand, etc.).
Tom